Researchers at Cornell University have unveiled a groundbreaking neural implant, measuring just 300 microns long and 70 microns wide—small enough to rest on a grain of salt. This innovative device, known as a microscale optoelectronic tetherless electrode (MOTE), can wirelessly transmit brain activity data from living animals for over a year. The findings were published on November 3, 2023, in the journal Nature Electronics.
The development of the MOTE is a significant leap in microelectronic systems, demonstrating the potential for neural monitoring and bio-integrated sensing at an unprecedented scale. Co-led by Alyosha Molnar, the Ilda and Charles Lee Professor in the School of Electrical and Computer Engineering, and Sunwoo Lee, an assistant professor at Nanyang Technological University, the project highlights the effective application of advanced technology in neuroscience.
The MOTE operates using red and infrared laser beams that effortlessly penetrate brain tissue, transmitting data back through tiny pulses of infrared light. These light pulses encode the brain’s electrical signals, with an aluminum gallium arsenide semiconductor diode capturing light energy to power the circuit and facilitate communication. This innovative design includes a low-noise amplifier and optical encoder, both constructed using semiconductor technology commonly found in microchips.
Alyosha Molnar remarked, “As far as we know, this is the smallest neural implant that will measure electrical activity in the brain and then report it out wirelessly.” He elaborated on the device’s efficiency, stating that it uses pulse position modulation—similar to the coding utilized in satellite communications—to transmit data while consuming minimal power.
The research team initially tested the MOTE on cell cultures before implanting it into the barrel cortex of mice, the brain region responsible for processing sensory information from whiskers. Over the year-long study, the implant successfully recorded neuron spikes and broader synaptic activity patterns, all while ensuring the mice remained healthy and active.
Molnar emphasized the need for such advancements, explaining, “Traditional electrodes and optical fibers can irritate the brain. The tissue moves around the implant and can trigger an immune response.” The team aimed to create a device small enough to minimize disruption while capturing brain activity more rapidly than conventional imaging systems, without requiring genetic modifications of the neurons.
Looking ahead, the MOTE’s unique material composition may enable the collection of electrical recordings from the brain during MRI scans, a feat not achievable with existing implants. Additionally, the technology could be adapted for use in other tissues, such as the spinal cord, and potentially integrated with future innovations, including optoelectronics embedded in artificial skull plates.
The concept for the MOTE was first proposed by Molnar in 2001, but substantive progress did not occur until he began collaborative discussions about a decade ago with members of Cornell Neurotech, a joint initiative between the College of Arts and Sciences and Cornell Engineering.
The research received support from the National Institutes of Health, with fabrication work conducted at the Cornell NanoScale Facility, which is backed by the National Science Foundation. Co-authors of the published paper include prominent figures such as Chris Xu, director of the School of Applied and Engineering Physics; Paul McEuen, John A. Newman Professor Emeritus in the Department of Physics; Jesse Goldberg, Dr. David Merksamer and Dorothy Joslovitz Merksamer Professor in Biological Sciences; and Jan Lammerding, professor in the Meinig School of Biomedical Engineering.
As the research continues to unfold, the MOTE represents a promising step forward in neuroscience, potentially transforming how brain activity is monitored and understood.
